Engine cold start emissions may contribute to a large portion of a total vehicle emissions. During some engine cold starts, an engine control strategy may include initiating cold start emissions reduction (CSER), wherein an engine calibration is altered such that a beginning of the cold start includes producing additional heat energy for a catalyst. This may include increased fuel injection volume and delayed spark timings to increase exhaust gas temperatures.
However, CSER calibrations are inherently inefficient due to heat loss to one or more of a turbocharger and an exhaust system upstream of the catalyst. Furthermore, increased fuel injection volumes increase particulate emissions relative to each injection. CSER may be desired outside of a beginning of a cold start to maintain a catalyst temperature. This results in increased particulate emissions that may necessitate inclusion of a particulate filter for meeting emissions standards, thereby increasing vehicle production costs.
Additional aftertreatment deficiencies may appear during electric hybrid applications for vehicles configured with a control strategy for operating in a fully electric mode (e.g., vehicle is propelled by an electric motor and is not propelled by combustion) while the hybrid vehicle's engine is not rotating. Thus, exhaust gas is not produced, resulting in a cooling of the catalyst. In this way, hybrid vehicle applications and propulsion via the electric motor may be limited in light of the cooling of the catalyst. This may decrease fuel economy.
Other attempts to address catalyst temperatures include electrically heating the catalyst via an electric heating element. During the cold start and other engine operating conditions where the catalyst temperature is less than a light-off temperature, the electric heating element may be activated. Similar to the problems described above, doing this may result in decreased fuel economy.
However, the inventors herein have recognized potential issues with such systems. As one example, the electric heating element consumes fuel and/or reduces a battery state of charge (SOC). As such, during hybrid vehicle applications utilizing an electric motor powered by a battery, heating the catalyst via the electric element may hamper an all-electric application of the hybrid vehicle. Additionally, electric heating elements are costly, resulting in increased production costs.
In one example, the issues described above may be addressed by a method comprising flowing lean exhaust gas from a first group of cylinders directly to a three-way catalyst, flowing rich exhaust gas from a second group of cylinders directly to a steam reforming catalyst, and flowing exhaust gas from the steam reforming catalyst to the three-way catalyst. In this way, an exothermic reaction between oxidants and reductants from the two separated exhaust gases may occur adjacent the three-way catalyst, thereby providing additional thermal energy to the three-way catalyst.
As one example, the first cylinder bank is coupled to a first exhaust passage and the second cylinder bank is coupled to a second exhaust passage. The first exhaust passage leads to at least the three-way catalyst, while the second exhaust passage leads to the steam reforming catalyst. In one example, where a three-way catalyst temperature is greater than a threshold temperature, exhaust gas flows directly from the first and second cylinder banks to the three-way catalyst. In other examples, where the three-way catalyst temperature is less than the threshold temperature, exhaust gas continues to flow directly from the first cylinder bank to the three-way catalyst while exhaust gas from the second exhaust bank directly to the steam reforming catalyst before it flows to the three-way catalyst. Additionally, the second cylinder bank may operate rich and the first cylinder bank may operate lean. By doing this, steam reforming reactions and water gas shift reactions may occur at the steam reforming catalyst, producing hydrogen gas (H2). H2 may combine and react with oxidizing species in the lean exhaust gas (e.g., O2, NO) at the three-way catalyst and release thermal energy. This may heat the three-way catalyst more rapidly than only relying on SCER adjustments.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.